1. Field of the invention
The present invention relates to lasers, and in particular, to metal vapor lasers, such as helium-cadmium lasers, wherein metal vapor typically condenses on an interior portion of the laser tube.
2. Description of the Prior Art
Metal vapor lasers, such as helium-cadmium lasers, have been commercially available, for a number of years.
Typically, metal vapor lasers use gas mixtures of two or more components as the active laser medium. When such a mixture is excited by a DC discharge, the component having the lowest ionization potential acquires a higher concentration of positive ions, free electrons carrying off the excess energy corresponding to the difference in energy between those levels.
A serious drawback of prior art metal vapor lasers was that the metal vapor deposited on the interior surfaces of the Brewster windows or laser mirrors as the tube operated. As a result, the laser output decreased and was eventually extinguished. Examples of prior art solutions for preventing cadmium condensation on the tube windows are disclosed in U.S. Pat. Nos. 3,614,658 and 3,624,548. In addition to condensing on the Brewster windows or laser mirrors, the metal vapor also deposits on and near the cool ends of the discharge tube. If not compensated for, the condensed cadmium forms a loose crystaline deposit with elongated extensions, or fingers, which grow to ultimately block the laser beam inside the plasma tube, which may build up and block the laser beam. However, no technique is currently available to remelt the cadmium condensate in He-Cd plasma tubes and thus this problem continues to adversely effect the lifetimes of these tubes.
What is thus desired is to provide a technique for melting the condensed metal which would otherwise interfere with the laser beam path in a more efficient and economical manner than is currently available.